Field of the Invention
The invention relates to a current-voltage regulator in particular for use in switched-mode power supplies.
Switched-mode power supplies are disclosed, for example, in Tietze and Schenk, "Electronics Circuits--Design and Applications," Springer 1991, pp. 502-10. Switched-mode power supplies of this type usually comprise a rectifier, a power switch for pulse width modulation, a filter and also a regulator for controlling the power switch. An input voltage (for example the rectified mains power supply voltage) is converted into a pulsed DC voltage with a variable duty ratio by the power switch acting as pulse width modulator. The pulse frequency may be variable or fixed in this case. The task of the regulator, then, consists in keeping the voltage at the output of the filter constant in a defined output current range. When the maximum output current is reached, the output current ought to be kept constant up to an output voltage of zero volts. The regulator must therefore process the voltage at the output of the filter and the current at the output of the filter as input variables and from them form a control signal for the power switch. The timing ratio of the switch is in this case influenced by the control signal.
In prior art regulators, the voltage-current comparison is in each case realized by means of an operational amplifier and also external resistance and capacitance networks. In this case, a current-voltage converter is usually connected upstream of the operational amplifier provided for the current comparison. The signals at the output of the operational amplifiers are thereby added and converted into a control current by means of a voltage-current converter. What is problematic in this case is the high outlay on circuitry and also the accuracy that can be achieved with integrated circuit technology.